Using the Stix finite element RF code to investigate operation optimization of the ICRF antenna on Alcator C-Mod

Journal Article · 24 August 2023 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/acee11 · OSTI ID:1996577

Migliore, C.  ^[1]; Wright, J. C.  ^[1]; Stowell, M.  ^[2]; Bonoli, P. T.  ^[1]

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1. Massachusetts Institute of Technology (MIT), Cambridge, MA (United States). Plasma Science and Fusion Center
2. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

As the ion cyclotron radio frequency range (ICRF) heating becomes more favorable in fusion devices, the urgency of predicting and mitigating impurity generation that arises from it becomes more pressing. In the ICRF regime, rectified RF sheaths are known to form at antenna and material edges that influence negative effects like sputtering and a decrease in heating efficiency. Methods to mitigate the formation of these RF sheaths through RF image currents cancellation have been experimentally studied. A power-phasing scan done on Alcator C-Mod in which the amount of power on the two inner straps ($$P_{in}$$) versus the total 4 straps ($$P_{tot}$$) was varied showed a minimization of enhanced potentials between $$P_{in}$$/$$P_{tot}$$ ~ 0.7 to 0.9 while impurities were minimized for $$P_{in}$$/$$P_{tot}$$ ~ 0.5 to 0.8. New capabilities in the realm of representing the RF sheath numerically now allow for these experiments to be simulated. Given the size of the sheath relative to the scale of the device, it can be approximated as a boundary condition (BC). A new parallelized cold-plasma wave equation solver called Stix implements a non-linear sheath impedance model BC formulated by J. Myra 2015 through the method of finite elements using the MFEM library [http://mfem.org]. It is seen that Stix shows qualitative agreement with the measured C-Mod enhanced potentials.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR). Scientific Discovery through Advanced Computing (SciDAC)
• Grant/Contract Number: AC52-07NA27344; SC0018090
• OSTI ID: 1996577
• Alternate ID(s): OSTI ID: 1994224; OSTI ID: 2229596
• Report Number(s): LLNL-JRNL-856342; 1084995; TRN: US2407481
• Journal Information: Nuclear Fusion, Vol. 63, Issue 10; ISSN 0029-5515
• Publisher: IOP ScienceCopyright Statement
• Country of Publication: United States
• Language: English